Yeah, when I got my boy he had a couple dull spots on his tail like that, and they're slowly going away with sheds. It's just basically the top layer of the scales that makes it shiny either came off with the previous shed or was underdeveloped. nothing to worry about!
1.0 Normal - Maynard
1.0 POG - Victor
0.1 YB - Diana
The scales are still there, they've just lost the shiny surface layer of cells. It'll be shiny again in another shed, and some other scales will be dull, because the snake rubbed its head in a slightly different place.